Island County climate

Island County Frost Dates and Growing Season

NOAA 1991-2020 normals for Coupeville 1 S, 1.7 km from Island County, elevation 50 ft

Frost and the growing season

NOAA's 1991-2020 freeze probabilities for Coupeville 1 S. A median date has an even chance of a later freeze in spring, or an earlier one in fall.

The last spring freeze typically comes around March 17 and the first fall freeze around November 11, a growing season of about 237 days.

Median at 36°F
last April 13, first October 27
Median at 32°F
last March 17, first November 11
Median at 28°F
last February 21, first November 28

Last freeze in spring

The chance of a later freeze than the date shown. At 10 percent, one spring in ten still freezes after the date; planting after the 10 percent date for 32°F is the cautious choice.

Threshold10%20%30%40%50%60%70%80%90%
36°FApr 30Apr 25Apr 20Apr 16Apr 13Apr 9Apr 5Apr 2Mar 27
32°FApr 3Mar 30Mar 26Mar 21Mar 17Mar 11Mar 7Mar 2Feb 24
28°FMar 12Mar 6Mar 1Feb 26Feb 21Feb 17Feb 11Jan 31Jan 11
24°FFeb 27Feb 18Feb 11Jan 31Jan 18Jan 8Jan 1Dec 22Dec 6
20°FFeb 15Jan 31Jan 16Jan 6Dec 31Dec 22Dec 13Dec 5Nov 28
16°FJan 12Jan 1Dec 25Dec 17Dec 11Dec 6Dec 3Nov 30Nov 23

First freeze in fall

The chance of an earlier freeze than the date shown. At 10 percent, one fall in ten freezes before the date.

Threshold10%20%30%40%50%60%70%80%90%
36°FOct 7Oct 14Oct 18Oct 22Oct 27Oct 30Nov 2Nov 6Nov 13
32°FOct 21Oct 30Nov 3Nov 7Nov 11Nov 16Nov 20Nov 25Dec 1
28°FNov 6Nov 12Nov 19Nov 24Nov 28Dec 1Dec 7Dec 16Dec 30
24°FNov 16Nov 25Nov 30Dec 5Dec 12Dec 19Dec 29Jan 6Jan 28
20°FNov 19Nov 28Dec 2Dec 9Dec 16Dec 24Jan 1Jan 14Feb 1
16°FNov 23Nov 29Dec 2Dec 6Dec 9Dec 15Dec 23Jan 1Jan 8

Growing season length

Days between the last spring and first fall freeze at each threshold, with the chance of a season at least that long.

Threshold10%20%30%40%50%60%70%80%90%
36°F219211204199194190185179171
32°F266255249243237232226221212
28°F321308299289281274267259249
24°F365357344335328320312303286
20°F365365365365365359344333321
16°F365365365365365365365365363

How often it gets that cold

The share of years with at least one night at or below each temperature.

36°F or colder
100% of years
32°F or colder
100% of years
28°F or colder
99% of years
24°F or colder
84% of years
20°F or colder
47% of years
16°F or colder
12% of years

Degree days

A degree day is one degree of the daily mean temperature beyond a base, for one day. Heating degree days count cold (the fuel a house burns), cooling degree days heat, growing degree days the warmth a crop needs; each crop has its own base.

Heating degree days, base 65°F
5,402
Cooling degree days, base 65°F
22
Growing degree days, base 40°F
3,940
Growing degree days, base 45°F
2,509
Growing degree days, base 50°F
1,420
Growing degree days, base 55°F
639
Growing degree days, base 60°F
166

Growing degree days by month, base 50°F

Heating and cooling by month

MonthHeating DDCooling DDGrowing DD 50
January76301
February65901
March63105
April477034
May3370135
June2212231
July12211353
August1137360
September2231229
October451062
November62708
December77801

What this means

NOAA computes these from the daily lows at the station over 1991-2020, fitting the dates of each year's last and first freeze to a distribution, so a date can be stated at any level of risk. 36°F is a frost risk for tender plants on a clear, calm night, since the ground cools below the air above it; 32°F is a freeze; 28°F is a hard freeze that kills most annuals.

The station is 1.7 km from Island County. Low ground, valleys and open fields freeze earlier and later than a town center or a hillside.

More

Sources

NOAA NCEI U.S. Climate Normals, 1991-2020, annual and seasonal normals for station USC00451783 (Coupeville 1 S). Public domain.